Non-plasma reaction apparatus and method

ABSTRACT

An apparatus and method for forming a self-limiting etchable layer on a workpiece. The apparatus comprises: a chamber adapted for holding a workpiece; a distribution plate within the chamber, wherein the distribution plate includes channels for introducing a first fluid (e.g., ammonia) and a second fluid (e.g., hydrogen fluoride) into the apparatus, such that the first and second fluids may be directed into the apparatus at the angles Î, 1  and Î, 2  with respect to an exposed surface of the distribution plate, wherein the channels for each type of fluid may be arranged respectively in alternating rings; and wherein each angle Î, 1  and Î, 2  are at least 45 degrees and less than 90 degrees, offset by Î± 2  and Î 2   2  and Î± 1  and Î 2   1  by analogy. The method for forming the etchable layer on the workpiece comprises introducing a first fluid and a second fluid into the chamber through the channels.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention generally relates to an apparatus andmethod for forming a surface film, and more particularly, to anapparatus and method for performing a non-plasma chemical reaction toform the surface film.

[0003] 2. Background Art

[0004] The ability to control etching by hydrogen fluoride (HF) to agiven thickness of a surface layer of a workpiece that has been adaptedfor etching is an important prerequisite for accurate etching in themanufacture of an integrated circuit (IC). The surface layer of theworkpiece may be adapted for etching by forming a surface layer that isan oxide of the material of the workpiece. If the workpiece comprisessilicon or germanium, the surface layer of the workpiece may be adaptedfor etching by forming the surface layer of silicon dioxide (SiO₂) orgermanium dioxide (GeO₂). Pure hydrogen fluoride (HF) may etch theadapted surface layer by forming gaseous silicon tetrafluoride (SiF₄).The gaseous SiF₄ is very volatile such that exposing the surface layerto HF readily etches the surface layer, thereby exposing a remaininglayer of oxide to etching by the HF. Etching to the given thickness isdifficult to control because the formation of SiF₄ continues until thesurface layer, i.e., the oxide layer, has been completely etched due toformation and evaporation of SiF₄.

[0005] In view of the need to control the etching thickness when theadapted surface layer of a workpiece is exposed to HF, there is a needfor an apparatus and method that provides controlled etching of theadapted surface layer with HF.

BRIEF SUMMARY OF THE INVENTION

[0006] The present invention provides an apparatus for forming aself-limiting etchable layer on a workpiece, comprising:

[0007] a chamber adapted for holding a workpiece, wherein a surfacelayer of the workpiece has been adapted for being etched; and

[0008] a distribution plate within the chamber, wherein the distributionplate comprises a first plurality of channels for providing a firstfluid to flow into the chamber at an angle Î,₁ with respect to anexposed surface of the distribution plate and a second plurality ofchannels for providing a second fluid to flow into the chamber at anangle Î,₂ with respect to the exposed surface of the distribution plate,and wherein the first plurality of channels and the second plurality ofchannels are arranged in rings around a common point of the distributionplate;

[0009] wherein the first fluid and the second fluid are adapted to reactinside the chamber to form a self-limiting etchable layer on a portionof the adapted surface layer of the workpiece.

[0010] A second embodiment of the present invention provides a methodcomprising:

[0011] providing a workpiece within a chamber, wherein a surface layerof the workpiece has been adapted for being etched;

[0012] providing a distribution plate over the workpiece, wherein thedistribution plate includes a first plurality of channels for providinga first fluid to flow into the chamber at an angle Î,₁ with respect toan exposed surface of the distribution plate and a second plurality ofchannels for providing a second fluid to flow into the chamber at anangle Î,₂ with respect to the exposed surface of the distribution plate,and wherein the first plurality of channels and the second plurality ofchannels are arranged in rings around a common point of the distributionplate; and

[0013] forming a self-limiting etchable layer by providing the first andsecond fluids over the adapted surface layer of the workpiece.

[0014] A third embodiment of the present invention provides adistribution plate comprising:

[0015] a first plurality of channels for providing a first fluid to flowinto a chamber at an angle Î,₁ with respect to an exposed surface of thedistribution plate; and

[0016] a second plurality of channels for providing a second fluid toflow into the chamber at an angle Î,₂ with respect to the exposedsurface of the distribution plate;

[0017] wherein the first plurality of channels and the second pluralityof channels are arranged in rings around a common point of thedistribution plate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0018]FIG. 1 depicts an exterior view of a single-substrate-processingnon-plasma reaction apparatus, according to embodiments of the presentinvention;

[0019]FIG. 2 depicts a top interior view of FIG. 1 after opening a lidof the apparatus and rotating it in a counter-clockwise direction on alongitudinal axis through a center of the apparatus;

[0020]FIG. 3 depicts a top view of an electrostatic chuck of theapparatus;

[0021]FIG. 4 depicts a longitudinal cross-sectional view taken alongline 4-4 of FIG. 1;

[0022]FIG. 5 depicts a cross-sectional view taken along line 5-5 of FIG.4 of a center portion of a distribution plate;

[0023]FIG. 6A depicts a cross-sectional view taken along line 6-6 ofFIG. 4 of a portion of the distribution plate;

[0024]FIG. 6B depicts FIG. 6A, wherein three dimensional XYZ axes aresuperimposed on the cross-sectional view depicted by FIG. 6A, takenalong line 6-6 of FIG. 4; FIG. 7 depicts an exploded frontal interiorview of the apparatus; and

[0025]FIG. 8 depicts a method for forming a self-limiting etchablelayer, according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention discloses an apparatus and method thatprovides controlled etching of an adapted surface layer of a workpieceor wafer by reaction of the adapted surface layer with ammoniumbifluoride (NH₅F₂), forming a self-limiting etchable layer, ammoniumhexafluorosilicate, (NH₄)₂SiF₆), that may be removed by thermaldesorption. NH₅F₂ may be formed by mixing a first fluid, ammonia (NH₃)and a second fluid, hydrogen fluoride (HF). The adapted surface layer onthe workpiece may comprise an oxide layer, formed by thermal oxidationor tetraethoxysilane (TEOS) oxidation of a portion of the surface of theworkpiece or wafer. Etching the adapted surface layer with HF alone to agiven thickness is difficult to control because the formation of SiF₄continues until the surface layer, i.e., the oxide layer, has beencompletely etched due to formation and evaporation of SiF₄. Reaction ofthe adapted surface layer with (NH₅F₂) forms the self-limiting etchablelayer, (NH₄)₂SiF₆), that provides controlled etching of an adaptedsurface layer of a workpiece or wafer because the self-limiting layerhas reduced permeability to HF in the NH₃ and HF mixture.

[0027] Jeng et al. disclose in commonly assigned U.S. Pat. No.5,282,925, herein incorporated by reference, a method for formation of aself-limiting etchable layer. Hereinafter, a self-limiting etchablelayer includes layers made of materials such as ammoniumhexafluorosilicate, (NH₄)₂SiF₆, that may become impervious to continuedexposure to hydrogen fluoride (HF), resulting in an ability to controlan etching thickness. In Jeng et al., a surface layer of a silicon waferis adapted to being etched by forming an oxide layer such as a silicondioxide (SiO₂) layer on the surface of the wafer. In Jeng et al., aportion of the SiO₂ layer becomes a self-limiting etchable layer whenthe portion of the layer of SiO₂ undergoes a non-plasma reaction withammonium bifluoride (NH₅F₂), producing the self-limiting etchable layerof (NH₄)₂SiF₆ and a remaining layer of unreacted SiO₂. According to Jenget al., NH₅F₂ may be produced by chemical combination of two (2) molesof HF and one (1) mole of ammonia (NH₃). Hereinafter, “providing astoichiometric number of moles of HF to NH₃ needed to form ammoniumbifluoride (NH₅F₂)” or “providing a stoichiometric molar ratio ofHF:NH₃=2 needed to form NH₅F₂” means providing two (2) moles of HF andone (1) mole of ammonia (NH₃) to form NH₅F₂.

[0028] Pure hydrogen fluoride (HF) may etch the adapted surface layer byforming gaseous silicon tetrafluoride (SiF₄). The gaseous SiF₄ is veryvolatile such that exposing the surface layer to HF readily etches thesurface layer, thereby exposing a remaining layer of oxide to etching bythe HF. Etching to the given thickness is difficult to control becausethe formation of SiF₄ continues until the surface layer, i.e., the oxidelayer, has been completely etched due to formation and evaporation ofSiF₄.

[0029] According to Jeng et al., the reaction of HF with SiO₂ when incontact with condensed ammonium bifluoride (NH₅F₂) is similar to thereaction in aqueous solution, SiO₂+4HF═SiF₄+2H₂O. However, instead ofbeing released to the solution, the SiF₄ product is trapped and reactswithin the condensed film to produce (NH₄)₂SiF₆. The (NH₄)₂SiF₆ isobserved in IR spectra of reacted layers. Microbalance results also showthe presence of the reacted layer. Condensation of NH₃ and HF followedby desorption of the unreacted excess produces a frequency decline of101 Hz, corresponding to reaction of 84 â,,<< of the several thousandangstrom thick layer of NH₅F₂ that initially condensed. After heating to100 Â° C. there is a 103 Hz increase of resonant frequency correspondingto 58 â,,<< of SiO₂ being etched from the adapted surface layer of thesilicon wafer.

[0030] Thermal desorption spectra are consistent with SiF₄ released uponthermal decomposition of the reacted layer of ammoniumhexafluorosilicate. The ammonium hexafluorosilicate layer can also beremoved by rinsing in a solvent, such as water.

[0031] According to Jeng et al., the amount of SiO₂ which may be etchedmay be controlled by providing a stoichiometric number of moles of HF toNH₃ needed to form ammonium bifluoride (NH₅F₂), i.e. providing a molarratio of HF to NH₃ in the gas above the SiO₂ surface substantiallyequivalent to 2. Pure HF etches SiO₂ with no self-limiting process.Ammonia (NH₃) is necessary to form the hexafluorosilicate product.

[0032] Jeng et al. discloses an apparatus and method in which ammoniumbifluoride (NH₅F₂) vapors can evaporate from an NH₅F₂ effusion cell,leading to a non-stoichiometric NH₅F₂ on the adapted surface layer beingetched. An object of the present invention is to provide an apparatusand method in which the stoichiometric molar ratio of HF:NH₃=2 needed toform NH₅F₂ may be substantially uniformly and homogeneously provided onthe adapted surface layer being etched.

[0033] In accordance with embodiments of the present invention, FIG. 1depicts an exterior view of a single-substrate-processing non-plasmareaction apparatus 10, comprising an outer wall 8 of the apparatus 10,an exhaust port 83, dual manometers 85 and 87 and a lid 90. The outerwall 8 of the apparatus 10 may comprise a surface 91. The lid 90comprises a surface 113 and a handle 95 on the surface 113. Theapparatus 10 may further comprise a hinge 93, wherein a portion 89 ofthe hinge 93 may be coupled to the surface 91 of the outer wall 8, aportion 86 of the hinge 93 may be coupled to the surface 113 of the lid90, and the portions 89 and 86 may be operatively coupled to a rotatingportion 84 of the hinge 93. The rotating portion 84 of the hinge 93 mayrotate on an axis parallel to the surface 91 of the wall 8 in adirection of an arrow 81. Referring to FIG. 1, the fluid feed line 99passes through the lid 90 and extends to a source of first or secondfluid (not shown) via a remaining portion of the fluid feed line 99within the apparatus 10 as depicted in FIG. 2 and described infra. In alike manner, the fluid feed line 97 passes through the lid 90 anddescribed herein and extends to a source of first or second fluid (notshown) via a remaining portion of the fluid feed line 97 within theapparatus 10 as depicted in FIG. 2 and described infra. The manometers85 and 87 may be used to measure a pressure within the chamber 7 due inpart to a flow of the first and second fluids through fluid feed lines97 and 99. The manometer 85 may have a range from about 0-100 milli torr(mT) and the manometer 87 may have a range from about 0-100 torr. Thefirst fluid may comprise, inter alia, ammonia (NH₃) and the second fluidmay comprise, inter alia, hydrogen fluoride (HF). The flow of NH₃ may beprovided to the fluid feed line 97 from about 3 to about 30 sccm at apressure from about less than 1 psi to about 40 psi, and a flow of theHF may be provided to fluid feed line 99 from about to about 60 sccm ata pressure from about less than 1 psi to about 5 psi. The fluid feedlines 97 and 99 may be alternatively provided with inter alia Argon orN₂ gas.

[0034]FIG. 2 depicts a top view of FIG. 1 after rotating the apparatus10 in a counter-clockwise direction on a longitudinal axis through acenter of the apparatus 10, such that the hinge 93 may be located at atop back position of the apparatus 10, and after lifting the lid 90 onthe hinge 93 of the apparatus 10. Lifting the lid 90, wherein therotating portion 84 of the hinge 93 was rotated 180 degrees in thedirection of the arrow 81, exposed a portion 66 of a surface of the lid90 that may be opposite and parallel to the surface 113 of the lid 90,as depicted in FIG. 1 and described herein. The exposed surface 66 ofthe lid 90 may further comprise portions of the fluid feed lines 97 and99 that may pass through the lid 90 as depicted in FIG. 1 and describedherein. Referring to FIG. 2, a distribution plate 40 having an exposedsurface 43 may be operatively coupled to the remaining portion (notshown) of a surface of the lid 90 that may be opposite and parallel tothe surface 113 of the lid 90, as depicted in FIG. 1 and describedherein. The distribution plate 40 may have been operably coupled to thelid 90 by inserting fasteners through holes 6.

[0035] The distribution plate 40 further comprises “I” rings, wherein Iis a positive integer greater than or equal to 2, and wherein the ringshave been denoted as R_(X) (X=1, 2, . . . ., I-1, I). FIG. 2 shows rings44, 46, 48, and 41, which are respectively denoted as R₁, R₂, R_(I-1),and R_(I). The rings R_(X) (X=1, 2,, . . . , I-1, I) each have a commonpoint P (i.e. point 49 in FIG. 2) on the surface 43 of the distributionplate 40, wherein P is within each R_(X) for values of X=1, 2, . . . ,I-1, I. Each ring R_(X) is totally within each ring R_(X)+1 for valuesof X=1, 2, . . . , (I-1).

[0036] Additionally, each ring R_(X) has a perimeter of length D_(X),(X=1, 2, . . . , I-1, I), such that D₁<D₂<. <D_(I). Corresponding pointsin rings R₁, R₂, . . . , R_(I) are at increasing distance from thecommon point P. Each ring R_(X)(X=1, 2, . . . , I) has any geometricalshape such as inter alia, a circle, an ellipse, a rectangle or a square,etc.

[0037] Each ring of the I rings R₁, R₂, . . . , R_(I) in FIG. 2comprises a distribution of channels 3 of a first type in which thefirst fluid may flow, or a distribution of channels 5 of a second typein which the second fluid may flow. There are n₁ channels 3 of the firsttype in the I rings collectively, and there are n₂ channels 5 of thesecond type in the I rings collectively. The first fluid from the fluidfeed line 97 flows through the n₁ channels 3 of the first type, and thesecond fluid from the fluid feed line 99 flows through the n₂ channels 5of the second type, as will be described infra in conjunction with FIG.4. A ring that comprises channels 3 of the first type is called a ringof the first type, and a ring that comprises channels 5 of the secondtype is called a ring of the second type. There are I₁ rings of thefirst type and I₂ rings of the second type such that I₁â%o¥1, I₂â%o¥1,and I=I₁+I₂. Thus the I₁ rings of the first type collectively comprisethe n₁ channels 3 of the first type and no channels 5 of the secondtype, and the I₂ rings of the second type collectively comprise the n₂channels 5 of the second type and no channels 3 of the first type. Forexample, with I=4 assumed, if I₁1=2 such that the I₁ rings compriserings R₁ and R₃ respectively having n₁₁ and n₁₃ channels 3 of the firsttype then n₁=n₁₁+n₁₃, and if I₂=2 such that the I rings comprise ringsR₂ and R₄ respectively having n₂₂ and n₂₄ channels 5 of the second type,then n₂=n₂₂+n₂₄. The first subscript “1” of n₁₁ and n₁₃ identifies thechannels 3 of the first type and the first subscript “2” of n₂₂ and n₂₄identifies the channels 5 of the second type. The second subscripts “1”and “3” of n₁₁ and n₁₃ identifies the channels 3 of the first type inthe rings R₁ and R₃ respectively. The second subscripts “2” and “4” ofn₂₂ and n₂₄ identifies the channels 5 of the second type in the rings R₂and R₄. Hereinafter, in the example with I=4 assumed, if I₁=2 such thatthe I₁ rings comprise rings R₁ and R₃ respectively having n₁₁ and n₁₃channels 3 of the first type and if I₂=2 such that the I₂ rings compriserings R₂ and R₄ respectively having n₂₂ and n₂₄ channels 5 of the secondtype, then the rings R₁, R₂, R₃ and R₄ are “alternating rings.” In ageneral case where I may be a positive integer greater than or equal to2, assuming I₁=I₂ and I₁+I₂=I, a number of alternating rings having n₁channels of the first type or n₂ channels of the second type is equal to½.

[0038] The I₁ rings of the first type and I₂ rings of the second typemay be arranged in any order with respect to the common point P. As afirst example with I assumed to be even, the I₁ rings of the first typeand the I₂ rings of the second type may alternate such that I₁=I₂,wherein the I₁ rings of the first type comprise rings R₁, R₃, . . . ,R_(I-1), and wherein the I₂ rings of the second type comprise rings R₂,R₄, . . . , R_(I). As a second example with I assumed to be odd, the I₁rings of the first type and the I₂ rings of the second type mayalternate such that I₁=I₂₊1, wherein the I₁ rings of the first typecomprise rings R₁, R₃, . . . , R_(I), and wherein the I₂ rings of thesecond type comprise R₂, R₄, . . . , R_(I-1). As a third example with Iassumed to be even, the I₁ rings of the first type may exist inconsecutive rings and the I₂ rings of the second type may likewise existin consecutive rings such that I₁=I₂, wherein the I₁ rings of the firsttype comprise rings R₁, R₂, . . . , R_(I/2), and wherein the I₂ rings ofthe second type R_(I/2+1), R_(I/2+2), . . . , R_(I). As a fourth examplewith I assumed to be odd, the I₁ rings of the first type may exist inconsecutive rings and the I₂ rings of the second type may likewise existin consecutive rings such that I=I₂+1, wherein the I₁ rings of the firsttype comprise rings R₁, R₂, . . . , R_((I+1)/2), and wherein the I₂rings of the second type comprise R_((1+1)/2+1), R_((I+1)/2+2), . . . ,R_(I). As a fifth example with I assumed to be odd, the I₁ rings of thefirst type may exist in consecutive rings and the I₂ rings of the secondtype may likewise exist in consecutive rings such that I₁=I₂−1, whereinthe I₁ rings of the first type comprise rings R₁, R₂, . . . ,R_((I−1)/2), and wherein the I₂ rings of the second type compriseR_((I−1)/2+1), R_((I−1)/2+2), . . . , R_(I).

[0039] Letting N_(x) denote the number of channels in ring R_(x)(X=1, 2,. . . , I), the scope of the present invention comprises several specialcases with respect to the number and distribution of channels in eachring. In a first special case, N_(x) increases monotonically as D_(x)increases. “Nx increases monotonically as Dx increases” means N_(x)always increases as D_(x) increases. In a second special case, N_(x)increases about linearly as D_(x) increases. In some embodiments, forexample, N_(x) is in a range of about 20 to about 72. In a third specialcase, the channels in each ring are approximately uniformly spacedapart. In some embodiments, a spacing between adjacent channels ofuniformly spaced channels in a ring may be in a range of, inter alia,about 0.0875 inches to about 0.104 inches.

[0040] Referring to FIG. 2, lifting the lid 90, wherein the rotatingportion 84 of the hinge 93 (see FIG. 1) was rotated 180 degrees in thedirection of the arrow 81, also resulted in exposing a chamber 7 of theapparatus 10. The chamber 7 of the apparatus 10 further comprises achamber wall 9 having an outer surface 12 and an inner surface 11. Aportion 101 of the fluid feed line 97 may be located in the wall 9. Thewall 9 may further comprise a portion 102 of the fluid feed line 99.

[0041] Referring to FIG. 2, the chamber 7 further comprises an upperannular ring 103 located such that a space or gap 107 exists between anedge 109 of the upper annular ring 103 and the inner surface 11 of thechamber wall 9. The upper annular ring 103 may be made frompolytetrafluoroethylene or fluorinated ethylene propylene such asTeflonÂ®, acetal homopolymer resin modified with DuPontâ,, KevlarÂ®resin such as DelrinÂ®, polyimide materials such as VespelÂ® orAltymidÂ®, polyetherimide materials such as UltemÂ®, polyarylate such asArdelÂ®, polycarbonate such as LexanÂ®, hard coated aluminum, stainlesssteel and combinations thereof. The apparatus 10 further comprises anelectrostatic chuck 110, wherein the electrostatic chuck 110 includes afeed line 117 for providing helium gas, grooves or glands 115 fordistributing the helium gas, and holes 120 for wafer support pins. Theelectrostatic chuck 110 is called an electrostatic chuck because itelectrostatically clamps onto a silicon wafer. The temperature of thewafer may be maintained from about −10Â° C. to about 90Â° C.

[0042]FIG. 3 depicts a top view of the electrostatic chuck 110 of FIG.2, further comprising a surface or a sandwich 119 that may include acopper sheath sandwiched between an upper and lower layer of Kaptontape. Alternatively, the tape may be any polyimide tape. Applying avoltage from about 0 to about 2,000 volts DC to the surface or thesandwich 119 may result in coulomb attraction that may attract a waferto the surface 119. The electrostatic chuck device may be obtained fromApplied Materials, Inc., 3050 Bowers Avenue, Santa Clara, Calif.95054-3299, U.S.A.

[0043]FIG. 4 depicts a cross-sectional view taken along line 4-4 of FIG.1, wherein the apparatus 10 further comprises the distribution plate 40,operatively coupled to the lid 90, wherein the surface 43 of thedistribution plate 40 faces away from the lid 90 and the surface 42 ofthe distribution plate 40 faces toward the lid 90. The distributionplate 40 may be operatively coupled to the lid 90 because the fluid feedline 97 has passed through the surface 113 as depicted in FIG. 1 anddescribed herein, and has been operatively coupled to a cavity or groove33 abutting the surface 42 of the distribution plate 40, and to the n₁channels 3 of the first type, as depicted in FIG. 2, and describedherein. FIG. 4 further depicts the fluid feed line 99 after it haspassed through the surface 113 as depicted in FIG. 2 and describedherein, and has been operatively coupled to a cavity or groove 55abutting the surface 42 of the distribution plate 40, and to the n₂channels 5 of the second type, as depicted in FIG. 2, and describedherein. The fluid feed line 97 provides the first fluid to the cavity orgroove 33 and the n₁ channels 3 of the first type and the fluid feedline 99 provides the second fluid to the cavity or groove 55 and the nchannels 5 of the second type.

[0044] The surface 42 of the distribution plate 40 may include a groove121 between the channels 3 and 5, wherein the groove 121 may furthercomprise a bottom wall 54, and wherein a depth of the groove 121 fromthe surface 42 to the bottom wall 54 may be at least 0.078 in. Thegroove 121 may include an o-ring or equivalent seal 123, wherein theseal 123 may prevent commingling of the first and second fluids in then₁ channels 3 of the first type and the n₂ channels 5 of the second typerespectively. An objective of the present invention is to have NH₃ andHF, inter alia, enter chamber 7 without pre-mixing. O-rings orequivalent seals 123 are used as barriers to prevent the fluids in eachring R_(X) from mixing. The o-ring or equivalent seals 123 may be madefrom polytetrafluoroethylene or fluorinated ethylene propylene such asTeflonÂ®, acetal homopolymer resin modified with DuPontâ,, KevlarÂ®resin such as DelrinÂ®, polyimide materials such as VespelÂ® orAltymidÂ®, polyetherimide materials such as UltemÂ®, polyarylate such asArdelÂ®, polycarbonate such as LexanÂ®, and combinations thereof. Thefirst and second fluids may be sent to alternating rings (i.e., thefirst and second fluids may be sent to rings R₁, R₃, R₅, . . . and R₂,R₄, R₆, . . . , respectively) so that as the first and second fluidsrespectively exit the channels 3 and 5 of each ring, there is nocommingling of the first and second fluids until they enter the chamber7 through the channels 3 and 5 of each ring.

[0045] The apparatus 10 further comprises a workpiece 30, wherein aportion 32 of the workpiece 30 has been adapted for being etched, and aremaining portion 31 has not been adapted. The workpiece 30 may compriseany semiconductor material such as silicon or germanium. The adaptedsurface layer 32 may be formed by oxidiation of the silicon or germaniumusing any appropriate method of oxidation. For example, the adaptedsurface layer 32 of the workpiece 30 may be an oxide formed fromtetraethoxysilane (TEOS) or alternatively from thermal oxidation. Theworkpiece 30 may be held in place by the electrostatic chuck 110.

[0046] A self-limiting etchable layer 50, having a surface 26,comprising ammonium hexafluorosilicate ((NH₄)₂SiF₆), has been formedfrom a portion of the adapted surface layer 32 of the workpiece 30,wherein a remaining portion 37 of the adapted surface 32 has becomeimpervious to etching by the first or second fluid, such as hydrogenfluoride (HF), because the remaining portion 37 has been protected fromHF by the self-limiting layer 50, as disclosed by Jeng et al. in U.S.Pat. No. 5,282,925, described herein.

[0047] A thickness of the self limiting layer 50 may be controlled,wherein a change of 1Â° in a temperature of the workpiece 30 equals a 17â,,<< etch rate change/minute, wherein the etch rate is directlyproportional to the increase in temperature, in the temperature rangefrom about −10 to about 90Â° C. A temperature controlling device 180such as, for example, an aluminum cathode may be provided to maintainthe temperature of the workpiece 30 within +/−1Â° C. in the range fromabout −10 to about 90Â° C. The apparatus 10 further comprises a baseflange 34 for supporting the temperature controlling device 180. Thechamber wall 9 may also be provided with heating or cooling lines 104 tomaintain the chamber wall 9 from about −10 to about 90Â° C.

[0048] Prior to forming the self-limiting etchable layer 50, thedistribution plate 40 has been aligned over the adapted surface layer 32of the workpiece 30. Hereinafter, “aligning the distribution plate 40”or “centering the distribution plate 40” or “the distribution plate 40has been aligned” over the adapted surface layer 32 of the workpiece 30means the center 163 of the cavity or groove 33, the center point 49 onthe surface 43 of the distribution plate 40, the center 1 of theapparatus 10, and the center 165 of the workpiece 30 are located aspoints on a line 56, wherein the line 56 may be orthogonal to thesurfaces 42 and 43 of the distribution plate 40 and the adapted surfacelayer 32 of the workpiece 30. The center 1 of the chamber 7 may be foundat an intersection of transversal lines 57. The center 49 of the surface43 of the distribution plate 40, and the center 26 of the workpiece 30may be determined to be at an intersection of the respective transversallines.

[0049] In addition to aligning the distribution plate 40 prior toforming the self-limiting etchable layer 50, the distribution plate 40may be positioned a distance T from the adapted surface layer 32 of theworkpiece 30. In an embodiment of the present invention, the distance Tfrom the surface 26 of the adapted surface layer 32 of the workpiece 30to the surface 43 of the distribution plate 40 includes from about ⅛ in.to about 3 Â½ in.

[0050] The chamber 7 of the apparatus 110 further comprises: the surfaceor sandwich 119 of the electrostatic chuck 110; the upper annular ring103; the cathode insulator 105; and the lower annular ring 125,containing a plurality of exhaust holes 127 for distributing an exhaustflow provided by a vacuum pump, such as a turbo pump, through theexhaust port 83. Referring to FIG. 4, in an embodiment of the presentinvention, an exhaust flow that originates from the exhaust port 83, asdepicted in FIG. 1 and described herein, may be distributed through theplurality of exhaust holes 127 of the lower annular ring 125, resultingin a uniform or homogeneous atmosphere of reactive fluids over theworkpiece 30 in the chamber 7. Hereinafter, “reactive fluids” includethe first fluid, the second fluid, wherein the first or second fluidsmay be ammonia (NH₃) or hydrogen fluoride (HF) and ammonium bifluoride(NH₅F₂) and combinations thereof. Providing the reactive fluids over theadapted surface layer 32 of the workpiece 30, as a uniform orhomogeneous atmosphere, forms the self-limiting etchable layer 50 thatincludes layers made of materials such as ammonium hexafluorosilicate((NH₄)₂SiF₆), that may become impervious to continued exposure tohydrogen fluoride (HF). Such imperviousness is the basis for the layer50 being a self-limiting etchable layer. When the exhaust flow from theexhaust port 83 is distributed through the plurality of holes 127 in thelower annular ring 125, instead of through a single exhaust port, it wasdetermined that a pressure of at least 4 torr may be provided withoutcausing a concentration gradient of the fluids in the atmosphere, as mayresult if the lower annular ring 125 consisted of a single port, becausethe self-limiting etchable layer 50 had a uniform thickness. In anotherembodiment, providing the space or gap 107 between the upper annularring 103 and the inner surface 11 of the chamber wall 9 restricted theexhaust flow from the exhaust port 83 and increased a concentration ofthe reactive fluids over the adapted surface layer 32, such that achange of 1 Â° C. equals a 17 â,,<< of etch rate change/minute, when theworkpiece 30 was maintained at a temperature from about −10 to about90Â° C., and while operating at a pressure of at least 4 torr. In someembodiments, for example, the space or gap 107 may be a distance fromthe edge 109 of the upper annular ring 103 to the inner surface 11 ofthe chamber wall 9 and may be at least ⅜ in. Referring to FIGS. 3 and 4,the workpiece 30 may be supported by lift pins that may be insertedthrough holes 120 of the surface 119 of the electrostatic chuck 110. Thedistribution plate 40, the o-rings 123, the upper annular ring 103, thecathode insulator 105 and lower annular ring 125 may be made frompolytetrafluoroethylene or fluorinated ethylene propylene such asTeflonÂ®, acetal homopolymer resin modified with DuPontâ,, KevlarÂ®resin such as DelrinÂ®, polyimide materials such as VespelÂ® orAltymidÂ®, polyetherimide materials such as UltemÂ®, polyarylate such asArdelÂ®, polycarbonate such as LexanÂ®, and combinations thereof.

[0051]FIG. 5 depicts a cross-sectional view taken along line 5-5 of FIG.4 of a center portion of the distribution plate 40 in which the cavityor groove 33 and the n₁ channels 3 of the first type in the distributionplate 40 are substantially in the same plane. The n₁ channels 3 of thefirst type have been adapted to provide a line or path 162 or 167 for afirst fluid to flow from the surface 43 of the distribution plate 40 atan angle Î,₁ with respect to the surface 43, wherein angle Î,₁ is atleast 45 degrees and less than ₉₀ degrees. The n₁ channels 3 of thefirst type have been adapted to provide a line or path 162 or a line orpath 167 for a first fluid to flow from the surface 43 of thedistribution plate 40 at the angle Î,₁. The first fluid flows throughthe n₁ channels 3 of the first type along the line or path 162 or theline or path 167 drawn through a center 77 of the n₁ channels 3 of thefirst type.

[0052]FIG. 6B depicts a cross-sectional view taken along line 6-6 ofFIG. 4 of a portion of the distribution plate 40 in which the cavity orgroove 55 and the n₂ channels 5 of the second type in the distributionplate 40 are substantially in the same plane. The n₂ channels 5 of thesecond type have been adapted to provide a line or path 175 for a secondfluid to flow from the surface 43 of the distribution plate 40 at anangle Î,₂ with respect to the surface 43, wherein Î,₂ is at least 45degrees and less than ₉₀ degrees. The n₂ channels 5 of the second typehave been adapted to provide a line or path 175 for a second fluid toflow from the surface 43 of the distribution plate 40 at the angle Î,₂.The second fluid flows through the n₂ channels 5 of the second typealong the line or path 175 drawn through the center 79 of the n₂channels 5. The angle Î, ₁(see FIG. 5) may be greater or less than Î,₂or the angle Î,₁ may be substantially equal to Î,₂.

[0053]FIG. 6A depicts FIG. 6B, wherein three dimensional XYZ axes aresuperimposed on the cross-sectional view depicted by FIG. 6B, takenalong line 6-6 of FIG. 4. The cross-sectional view is a view of thedistribution plate 40, wherein an X axis is parallel to the surfaces 42and 43 of the distribution plate 40, a Y axis is perpendicular to the Xaxis in the same plane as the X axis and a Z axis, orthogonal to the Xand Y axes and to the cross-sectional view of the distribution plate 40.The right triangle ABO is in the XY plane. The line AB of the righttriangle ABC is also in the XY plane. However, the line or path 175drawn through the center 79 of the n₂ channels 5 of the second type maybe offset by an angle DAC 215 equal to Î±₂ with respect to the plane XYas it exits the surface 43 of the channels 5. The same line or path 175drawn through the center 79 of n₂ channels 5 of the second type may beoffset by an angle BAC 220 equal to Î² ₂ with respect to the XY plane.The offset angles Î±₂ and Î² ₂ with respect to the plane XY may be fromabout 0 to −45 and about 0 to +45 degrees with respect to the XY planeof the cross-sectional view.

[0054] Alternatively, by analogy to offsetting the line or path 175drawn through the center 79 of the n₂ channels 5 of the second type bythe angle DAC 215 equal to Î±₂ with respect to the plane XY as it exitsthe surface 43 of the channels 5 as in FIG. 6A, supra, referring to FIG.5, the line or path 162 drawn through the center 77 of the n₁ channels 3of the first type may be offset by an angle equal to Î±₁ by analogy tothe angle DAC 215 with respect to the XY plane, as depicted in FIG. 6A.The same line or path 162 drawn through the center 77 of n₁ channels 3of the first type may be offset by an angle equal to Î² ₁ by analogy tothe angle BAC 220 with respect to the XY plane, as depicted in FIG. 6A.The offset angles Î±₁ and Î² ₁ with respect to the plane XY may be fromabout 0 to −45 and about 0 to +45 degrees with respect to the XY planeof the cross-sectional view.

[0055] Referring to FIGS. 5 and 6B, offsetting the angle Î,₁ by Î±₁ andÎ² ₁ and the angle Î,₂ by Î±₂ and Î² ₂ respectively, increase mixing ofthe first and second fluids after they have been introduced into thechamber 7, as depicted in FIG. 4 and described herein. Referring to FIG.4, a flow distribution pattern of fluids from channels 3 and 5 may flowfrom the surface 43 through the space or gap 107 and exhaust holes 127.In theory, the flow pattern forms a vortex flow distribution whichfurther increases mixing of the two fluids. Referring to FIGS. 5 and 6B,it has been determined that a more uniform thickness of theself-limiting layer 50 resulted when the lines or paths 162, 167 and 175have been directed at angles Î,₁ or Î₂ that may be at least 45 degreesand less than ₉₀ degrees with respect to the surface 43, wherein theangle Î,₁ has been offset by Î±₁ and Î² ₁ or the angle Â±₂ has beenoffset by Î±₂ and Î² ₂, than if the lines or paths 162, 167 and 175 havebeen directed orthogonal to the surface 43.

[0056] Referring to FIG. 4, the cavity or groove 33 and the n₁ channels3 of the first type and cavity or groove 55 and the n₂ channels 5 of thesecond type may be formed in the distribution plate 46, such as bymechanical drilling, laser drilling or a chemical process.

[0057] Referring to FIGS. 5 and 6B, the flow rate (F) of the first orsecond fluid through the n₁ channels 3 of the first type and the n₂channels 5 of the second type may be proportional to factors such as thepressure of the first and second fluids, the pressure (vacuum) in thechamber, described herein in text associated with FIG. 2. In addition itmay be determined that F is inversely proportional to a volume (V) ofthe n₁ channels 3 of the first type or the n₂ channels 5 of the secondtype. The inversely proportional relationship between F and V of thechannels 3 and 5 may be expressed by the following formula 1:

F=1/V  1.

[0058] V may be calculated if the channels 3 and 5 are cylindrical,wherein V=Ï

R²H, wherein 2R₃=a diameter (D₃) of the n₁ channels 3 of the first typeor 2R₅=a diameter (D₅) of the n₂ channels 5 of the second type andwherein H is equal to a height of the cylinder. The inverselyproportional relationship between F and D, and H of the channels 3 and 5may be expressed by the following formula 1:

F=4/(

Ï

D ² H _(v))

[0059] Referring to FIG. 6B, the channels 5 may be cylindrical, having adiameter D₅ and a height H₅ described by the length of a portion BE ofthe line or path 175. By analogy the channels 3 in FIG. 5 may also becylindrical, having a diameter D₃ and a height H₃. The flow rate (F)through the channels 3 or 5 will be inversely proportional to D₂ andH_(X) (where X=3 or 5), according to Formula 2.

[0060] Referring to a right triangle AFE and a right triangle ACB inFIG. 6B, H₅ of the channels 5 (or H₃ of the channels 3, by analogy) is aportion BE of a hypotenuse AE of the triangle AFE when the channels 5start at the bottom 51 of the cavity or groove 55 and H₅ is thehypotenuse AE of the triangle AFE when the channels 5 extend from thesurface 42 to the surface 43 of the distribution plate 40. Referring toFormula 2 supra wherein F is inversely proportional to H_(X), a ratioAE/BE is an increased flow factor because flow may increase when BEdecreases. A ratio of AB/AE=AC/AF may be determined because a sine ofthe angle Î,₂ is equal to AF/AE and a sine of the angle Î,₂ is alsoequal to AC/AB. AC may be a length from the surface 42 to the bottom 51of the cavity or groove 55. AF may be a thickness of the distributionplate 40. Since AE=AB+BE, AB=AE−BE. Substituting for AB in the equalityAB/AE=AC/AF, (AE−BE)/AE=AC/AF. Factoring out AE from the left side of(AE−BE)/AE=AC/AF results in (1−BE/AE)=AC/AF, therefore BE/AE=AC/AF+1. Itmay be determined that a portion BE of the line or path 175 for thesecond fluid to flow from the bottom 51 of the cavity or groove 55 ofthe distribution plate 40 to the surface 43 of the distribution plate 40at the angle Î,₂ is a portion of a hypotenuse AE of the right triangleAFE. It may also be determined that a portion AB of the line or path 175would be the line or path 175 for the second fluid to flow from thesurface 42 of the distribution plate 40 to the channel 5 absent thecavity or groove 55. Therefore trigonometry may be used to determine arelationship between the flow of the first or second fluids through thechannels 5 (and by analogy, through the channels 3), a depth of thecavity or groove 55, and the angle Î.

[0061] In FIG. 6B, a triangle AFE has been formed by lines AF, FE and AEthat includes a triangle ACB that has been formed by lines AC, CB, andBA. Line AF is a thickness of the distribution plate 40, line FE is aportion of the surface 43 of the distribution plate 40, and line AE is alength (H_(T)) of channel 5 that the first or second fluids would haveto traverse absent cavity or groove 55. Line AB is a length (H_(A)) ofchannel 5 that the first or second fluids will not have to traversebecause of the cavity or groove 55. Line AC is a depth of the cavity orgroove 55 equal to a length (L) from the surface 42 to the bottom 51 ofthe cavity or groove 55. Line AF is a thickness (Y) of the distributionplate, i.e., an orthogonal length from the surface 42 to the surface 43of the distribution plate 40.

[0062] In embodiments of the present invention, referring to Formulas 1and 2 and FIGS. 5 and 6B, a diameter (D_(G)) of the cavities or grooves33 and 55 may be greater than a diameter (D_(C)) of the channels 3 and5, such that a volume VG of the cavities or grooves 33 and 55 may begreater than a volume V_(C) of the channels 3 and 5, such that a ratioof V_(G)/V_(C) is greater than 1. In an embodiment, for example, a depthof the cavity or groove 55 (or by analogy, a depth of the cavity orgroove 33 depicted in FIG. 5) from the surface 42 of the distributionplate 40 to a bottom wall 51 may be from about 0.3 to about 1.3 in., anda diameter (D_(C)) of the n₁ channels 3 of the first type may be atleast {fraction (30/1000)} in.

[0063]FIG. 7 depicts an exploded frontal interior view of the apparatus10 of FIG. 1, and comprises: O-rings 123 that provide a seal to preventcommingling of the n₁ channels 3 of the first type and n₂ channels 5 ofthe second type; the distribution plate 40, the electrostatic chuck 110,the upper baffle 103, the cathode insulator 105, and a lower annularring 125, containing a plurality of exhaust holes 127 for distributingthe exhaust flow provided by the exhaust port 83. Referring to FIG. 4,in an embodiment of the present invention, an exhaust flow thatoriginates from the exhaust port 83 may be distributed through theplurality of exhaust holes 127 of the lower annular ring 125, resultingin a uniform or homogeneous atmosphere of reactive fluids over theworkpiece 30 in the chamber 7. Hereinafter, “reactive fluids” includethe first fluid, the second fluid, wherein the first or second fluidsmay be ammonia (NH₃) or hydrogen fluoride (HF) and ammonium bifluoride(NH₅F₂) and combinations thereof. Providing the reactive fluids over theworkpiece 30, having the adapted surface layer 32, as a uniform orhomogeneous atmosphere forms the self-limiting etchable layer 50 thatincludes layers made of materials such as ammonium hexafluorosilicate,(NH₄)₂SiF₆, that may become impervious to continued exposure to hydrogenfluoride (HF). Such imperviousness is the basis for terming the layer 50a self-limiting etchable layer. When the exhaust flow from the exhaustport 83 is distributed through the plurality of holes 127 in the lowerannular ring 125, instead of through a single exhaust port 83, apressure of at least 4 torr may be provided without causing aconcentration gradient of the fluids in the atmosphere, as may result ifthe lower annular ring 125 consisted of a single port. In anotherembodiment, the space or gap 107 exists between the upper annular ring103 and the inner surface 11 of the chamber wall 9. A purpose of thespace or gap 107 between the upper annular ring 103 and the innerchamber wall 11 is to act as a restriction in the exhaust flow, suchthat a concentration of the reactive fluids may be increased, whileoperating at a pressure of at least 4 torr. In some embodiments, forexample, the space or gap 107 may be at least ⅜ in. The distributionplate 40, the o-rings 123, the upper annular ring 103, the cathodeinsulator 105 and lower annular ring 125 may be made frompolytetrafluoroethylene or fluorinated ethylene propylene such asTeflonÂ®, acetal homopolymer resin modified with DuPontâ,, KevlarÂ®resin such as DelrinÂ®, polyimide materials such as VespelÂ® orAltymidÂ®, polyetherimide materials such as UltemÂ®, polyarylate such asArdelÂ®, polycarbonate such as LexanÂ®, and combinations thereof.

[0064]FIG. 8 depicts a method 200 for forming a self-limiting etchablelayer 50 as in FIG. 4, wherein the self-limiting etchable layer 50 maybe formed by reacting the oxide coating such as silicon dioxide orgermanium dioxide with a first fluid NH3 and a second fluid HF. Jeng etal. disclosed in U.S. Pat. No. 5,282,925, herein incorporated byreference, that when the first and second fluids are NH₃ and HF, theself-limiting etchable layer may be ammonium hexafluorosilicate.According to embodiments of the present invention, an average 1 sigmauniformity in a thickness of the self-limiting etchable layer 50 is1.2%, compared to an average 1 sigma uniformity in a thickness of theself-limiting etchable layer of 1.7% using the method and apparatus ofJeng et al. The average 1 sigma uniformity is defined as one (1)standard deviation of a mean thickness of the layer 50, expressed as apercent of the mean thickness. Further, a 20% improvement in processpressure range is obtained in the present invention compared to themethod and apparatus of Jeng et al. Using the same measurement tool, thesame monitors and substantially similar process conditions, the average1 sigma uniformity of a 166.14 â,,<<self-limiting etchable layer 50 issubstantially 0.84% using the apparatus 10, as depicted herein and themethod 200 of the present invention, compared to the average 1 sigmauniformity of a 95.5 â,,<< self-limiting etchable layer 50 issubstantially 1.4% using the method and apparatus of Jeng et al.

[0065] Referring to FIG. 8, the method 200 comprises the steps 210, 220,230, and 240. Step 210 provides a workpiece 30 within a chamber 7,wherein a surface layer of the workpiece 30 has been adapted for beingetched. Step 220 provides a distribution plate 40 over the workpiece 30,wherein the distribution plate 40 includes n₁ channels 3 of a first typeand n2 channels 5 of a second type, wherein the channels 3 of the firsttype have been adapted to provide a path for a first fluid to flow intothe chamber at an angle Î,₁ with respect to an exposed surface 43 of thedistribution plate 40, wherein the channels 5 of the second type havebeen adapted to provide a path for a second fluid to flow into thechamber 7 at an angle Î,₂ with respect to the exposed surface 43 of thedistribution plate 40, wherein the channels 3 of the first type and thechannels 5 of the second type may be arranged in alternating rings 44,46, 48, and 41 around a center of the distribution plate 40, as depictedin FIG. 2 and described in associated text supra, and wherein each angleÎ,₁ and Î,₂ is equal to 45 degrees and less than ₉₀ degrees. Step 230provides a first and second fluid to the distribution plate. Step 240forms the self-limiting etchable layer 50 on the workpiece 30 asdepicted in FIGS. 4-7 and described in associated text supra. Reactionof the NH₅ F₂ with a portion 35 of the adapted surface layer 32 formed aself-limiting etchable layer 50 of ammonium hexafluorosilicate on theworkpiece 30, wherein a thickness of the self-limiting layer 50 was atleast two-fold or at least twice as thick as the portion 35 of theadapted surface layer 32 from which portion 35 of the self-limitinglayer 50 was made. In some embodiments of the present invention, thethickness of the self-limiting etchable layer 50 was from about 100 toabout 300 â,,<<.

[0066] Described herein is an apparatus 10 as depicted in FIGS. 1-7 anddescribed in associated text supra for rapid delivery and homogeneousmixing of NH₃ and HF gas with the option of an elevated substratetemperature, in accordance with the method 200 as depicted in FIG. 8 anddescribed in associated text supra.

EXAMPLE 1

[0067] Referring to FIG. 8, the following experiment was performed inaccordance with the method 200.

[0068] Step 210, providing a workpiece 30 within a chamber 7, wherein asurface layer of the workpiece 30 has been adapted for being etched, asin FIG. 4:

[0069] A. Referring to FIG. 4, a workpiece 30 having a surface layer 32that had been adapted for being etched was provided in the apparatus 10.The workpiece 30 was electrostatically held in place on a surface 119 ofan electrostatic chuck 110. A polytetrafluoroethylene cathode insulator105 was wrapped around the cathode 180. The polytetrafluoroethylene ofthe cathode insulator 105 was at least about Â{fraction (1/2)} inchthick and insulated the cathode 180 to maintain a constant temperatureof the workpiece 30 to within +/−1Â° C. in a temperature range fromabout −10 to about 90Â° C.

[0070] Step 220, providing a distribution plate 40 over the workpiece30:

[0071] A. Referring to FIG. 4, a distribution plate 40 was provided suchthat the distribution plate 40 was aligned over the workpiece 30. Thedistance separating the surface 43 of the distribution plate 40 and theadapted surface layer 32 of the workpiece 30 was 2⅜ inches. Referring toFIG. 2, the distribution plate 40 included the rings 44, 46, 48, and 41,wherein the first ring 44 from the center point 49 included 20 channels3, the second ring 46 from the center point 49 included 36 channels 5,the third ring 48 from the center point 49 included 60 channels 3, andthe fourth ring 42 from the center point 49 included 72 channels 5. Thechannels 3 were adapted to provide a path for NH₃ to flow into thechamber 7 at an angle Î,₁=45 degrees with respect to an exposed surface43 of the distribution plate 40. The channels 5 were adapted to providea path for a HF to flow into the chamber at an angle Î,₂=45 degrees withrespect to the exposed surface 43 of the distribution plate 40. Thechannels 3 and 5 were arranged in alternating rings around the center 49of the distribution plate 40.

[0072] Step 230 providing a first and second fluid to the distributionplate 40:

[0073] A. A thickness of the self-limiting etchable layer 50 wascontrolled by varying the temperature of the workpiece 30, resulting incontrolling a reaction temperature between the HF and NH₃, or byaltering the HF:NH₃ stoichiometry. It was determined that a change of1Â° C. equals 17 Â,,<<of etch rate change/minute, when the workpiece 30was maintained at a temperature from about −10 to about 90Â° C., asdescribed in step 210 infra.

[0074] B. Referring to FIG. 4, providing a vacuum from 1 to about 100 mtfrom exhaust port 83 to the lower annular ring 125, containing theplurality of exhaust holes 127 for distributing the vacuum and providingchamber 7 with a flow of NH₃ and HF from the channels 3 and 5 of thedistribution plate 40 resulted in a vapor pressure of at least 4 torr.The flow of NH₃ was provided in a range of from about 3 to about 30 sccmfrom fluid line 97, and a flow of the HF was provided in a range fromabout 10 to about 60 sccm from fluid line 99. Referring to FIG. 4, thechamber 7 may optionally be provided with Argon or N₂ gas from about 0to about 100 sccm from the lines 97 and 99.

[0075] Step 240, forming the self-limiting etchable layer 50 on theworkpiece 30:

[0076] A. Referring to FIG. 4, a mixing was created as the NH₃ and HFenter the chamber 7 from the channels 3 and 5 and are pulled toward theexhaust holes 127 of the lower annular ring 125. The mixing wasaccomplished by directing the NH3 and HF at angles Î,₁ or Î,₂ withrespect to the exposed surface 43 of the distribution plate 40, whereinangles Î,₁ or Î,₂ were at least 45 degrees and less than ₉₀ degrees.Providing a vapor pressure of the HF and NH₃ of at least 4 torr as instep 230 provided a stoichiometric amount of HF to NH₃, substantiallyequal to 2, that resulted in formation of ammonium bifluoride (NH₅F₂) inthe chamber 7 over the adapted surface layer 32 of the workpiece 30.Reaction of the NH₅F₂ with a portion 35 of the adapted surface layer 32formed a self-limiting etchable layer 50 of ammonium hexafluorosilicateon the workpiece 30, wherein a thickness of the self-limiting layer 50was at least two-fold or at least twice as thick as the portion 35 ofthe adapted surface layer 32 from which portion 35 the self-limitinglayer 50 was made. In some embodiments of the present invention, thethickness of the self-limiting etchable layer 50 was from about 100 toabout 300 â,,<<.

[0077] The foregoing description of the preferred embodiments of thisinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed, and obviously, manymodifications and variations are possible. Such modifications andvariations that may be apparent to a person skilled in the art areintended to be included within the scope of this invention as defined bythe accompanying claims.

What is claimed is:
 1. An apparatus comprising: a chamber adapted forholding a workpiece having a surface layer adapted for being etched; anda distribution plate including a first plurality of channels forproviding a first fluid to flow into the chamber at an angle Î,₁ withrespect to an exposed surface of the distribution plate and a secondplurality of channels for providing a second fluid to flow into thechamber at an angle Î,₂ with respect to the exposed surface of thedistribution plate; wherein the first plurality of channels and thesecond plurality of channels are arranged in rings around a common pointof the distribution plate.
 2. The apparatus of claim 1, wherein eachangle Î,1 and Î,2 is at least 45 degrees and less than ₉₀ degrees. 3.The apparatus of claim 2, wherein paths of the first plurality ofchannels and paths of the second plurality of channels originate in anXY plane of the distribution plate and wherein each angle Î,₁ and Î,₂ isat least 45 degrees and less than ₉₀ degrees with respect to the XYplane and wherein each angle Î,₁ is offset from the XY plane at anoffset angle Î±₁ and Î² ₁ with respect to the XY plane, and wherein eachangle Î,₂ is offset from the XY plane at an offset angle Î±₂ and Î² ₂with respect to the XY plane, and wherein Î±₁, Î² ₁, Î±₂, and Î² ₂ areselected from the group consisting of from about 0 to −45 and from about0 to +45 degrees with respect to the XY plane.
 4. The apparatus of claim1, wherein the distribution plate comprises a material selected from thegroup consisting of polytetrafluoroethylene, fluorinated ethylenepropylene, acetal homopolymer resin, polyimide, polyetherimide,polyarylate, polycarbonate, and combinations thereof.
 5. The apparatusof claim 1, wherein the rings of the first and second types areconcentric rings, wherein each ring has a diameter from about 1.75inches to about 7.04 inches.
 6. The apparatus of claim 1, wherein thepaths of the fluids through the distribution plate further comprisesgrooves and wherein a volume of the grooves is greater than a volume ofthe channels.
 7. The apparatus of claim 1, wherein the rings around thecenter point of the distribution plate have shapes selected from thegroup consisting of circles, ellipses, rectangles, squares andcombinations thereof.
 8. The apparatus of claim 1, wherein the chamberfurther comprises a lower annular ring that includes a plurality ofholes extending over an exhaust port.
 9. The apparatus of claim 1,wherein the chamber further comprises an upper annular ring, wherein aspace is created between an edge of the upper annular ring and a wall ofthe chamber, and wherein the space restricts a flow of fluids in thechamber.
 10. The apparatus of claim 9, wherein the opening between theupper annular ring and either the workpiece or the chamber wall is atleast {fraction (3/8)} inch.
 11. The apparatus of claim 1, wherein thedistribution plate is located from about {fraction (1/8)} inch to about3 Â{fraction (1/2)} inches from a surface of the workpiece.
 12. Theapparatus of claim 1, the first fluid comprises ammonia gas and thesecond fluid comprises hydrogen flouride gas, the first fluid and thesecond fluid are adapted to react inside the chamber to form aself-limiting etchable layer on a portion of the adapted surface layerof the workpiece.
 13. A method, comprising: providing a workpiece withina chamber, wherein a surface layer of the workpiece has been adapted forbeing etched; providing a distribution plate over the workpiece, thedistribution plate including a first plurality of channels for providinga first fluid to flow into the chamber at an angle Î,₁ with respect toan exposed surface of the distribution plate and a second plurality ofchannels for providing a second fluid to flow into the chamber at anangle Î,₂ with respect to the exposed surface of the distribution plate,wherein the first plurality of channels and the second plurality ofchannels are arranged in rings around a common point of the distributionplate; and forming a self-limiting etchable layer on the surface layerof the workpiece.
 14. The method of claim 13, wherein each angle Î,₁ andÎ,₂ is at least 45 degrees and less than ₉₀ degrees.
 15. The method ofclaim 13, wherein the paths of the first plurality of channels and thepaths of the second plurality of channels originate in an XY plane ofthe distribution plate and wherein each angle Î,₁ and Î,₂ is at least 45degrees and less than ₉₀ degrees with respect to the XY plane andwherein each angle Î,₁ is offset from the XY plane at an offset angleÎ±1 and Î²1 with respect to the XY plane, and wherein each angle Î,₂ isoffset from the XY plane at an offset angle Î±₂ and Î² ₂ with respect tothe XY plane, and wherein Î±₁, Î² ₁, Î±₂, and Î² ₂ are each selectedfrom the group consisting of from about 0 to −45 degrees and from about0 to +45 degrees with respect to the XY plane.
 16. The method of claim13, wherein a thickness of the self-limiting etchable layer is at leasttwice as thick as a thickness of a portion of the adapted surface of theworkpiece from which portion the self-limiting etchable layer wasformed.
 17. A distribution plate comprising: a first plurality ofchannels for providing a first fluid to flow into a chamber at an angleÎ,₁ with respect to an exposed surface of the distribution plate; and asecond plurality of channels for providing a second fluid to flow intothe chamber at an angle Î,₂ with respect to the exposed surface of thedistribution plate; wherein the first plurality of channels and thesecond plurality of channels are arranged in rings around a common pointof the distribution plate.
 18. The distribution plate of claim 17,wherein each angle Î,1 and Î,2 is at least 45 degrees and less than ₉₀degrees.
 19. The distribution plate of claim 17, wherein the paths ofthe first plurality of channels and the second plurality of channelsoriginate in an XY plane of the distribution plate and wherein eachangle Î,₁ and Î,₂ is at least 45 degrees and less than ₉₀ degrees withrespect to the XY plane and wherein each angle Î,₁ is offset from the XYplane at an offset angle Î±₁ and Î² ₁ with respect to the XY plane, andwherein each angle Î,₂ is offset from the XY plane at an offset angleÎ±₂ and Î² ₂ with respect to the XY plane, and wherein Î±₁, Î² ₁, Î±₂,and Î² ₂ are selected from the group consisting of from about 0 to −45and from about 0 to +45 degrees with respect to the XY plane.
 20. Thedistribution plate of claim 17, wherein the first fluid is provided tothe first plurality of channels and the second fluid is provided to thesecond plurality of channels without premixing of the first and secondfluids.